Selected Posts from the Midd Blogosphere

Tag Archives: drought

It’s not your imagination, the leaves are turning early this year. The reason will seem a little odd, but an understanding of a tree’s relation to time helps.

I feel for scientists that have trouble explaining the concept of time. We are lineal creatures, stuck watching time pass from one year to the next. As a horticulturist, my year goes from spring to spring. But anthropologists measure civilizations in centuries, not our ordinary years. How about geologists, counting back years by the billions. Most impressive, let’s talk about Astronomy. A light year-the time and distance it takes for a photon of light to travel. It’s called the speed of light for a reason.

Tree time moves differently. Trees do everything slowly-germinate, grow, mature, reproduce, even die. Some varieties live well within one of our short lifetimes, while others will live for generations. Time moves in fits and starts for a tree, on yearly cycles familiar to those in Agriculture. But they aren’t exactly lineal.

Remember last year? It was a growing season in a bitter drought, with no rain for most of the spring, all of summer, not breaking until late in the fall. It was hot, dry, and overall not very pleasant. I use our annual flowers we plant as a barometer, and the ones we planted around campus languished in the heat, and with the exception of some petunias none ever really amounted to much.

Our tree canopy looked OK though, and we had a nice fall. But this year, not so much. Maples are turning early, losing their already smaller than normal leaves about 4 weeks too soon. Oaks have been thin all year, with many dead twigs and branches. But it was a great growing season this year, with all flowers blooming non-stop since commencement. But not in tree time.

Sugar Maple by Battel-August 30

Trees are about a year off, marking time in their own way. They leaf out and grow all season, but reach back to the previous year’s sugars and energy stored from the prior growing season. Last year’s food is this years energy. So the drought last year certainly affected the growth of trees, but on tree time it doesn’t show up until this year. Weakened roots and inadequate resources in twigs and stems are stunting growth this year, and trees are wearing out and starting to turn early. Trees live a dual year, growing in the previous year while stockpiling for the next.

Same Maple as Above-September 18

Ordinarily in the early fall there are always a couple of trees starting to turn, and the easy answer is that they are weakened, stressed trees, our canary in the coal mine showing us underlying problems we might not have seen. Usually the Black maples east of Old Chapel turn fall color early, a problem of not only age but poor soil and compaction from living in a college quad for 200 years. This year, though, it is many, many trees. Primarily sugar maples, and mostly middle-aged trees, I’d guess 40-75 years old. In tree time for a maple you can think of them as 30-year olds facing a mid-life crisis with all the associated baggage. Primarily we’ve seen trees turning this year as ones in poor soil, either on ledge, or heavy clay. Above my house on Snake Mountain I see the canopy turning color, the relatively young forest showing it’s stress.

Snake Mountain, first Week of September

Younger, less mature trees are probably more in balance, and also flaunt vigorous and resilient root systems, while old, mature veterans had the massive underground roots to weather the (lack of) storms. Neither are showing the stress or are turning early.

It’s too soon to say what the fall will bring for color, but I’d sure like to see a little more rain soon, and a break in this mini heat spell we’re having. I do predict an early season, though, maybe longer if the oaks in the lower elevations can hang in there.

The drought continues here on campus, and in the broader Champlain Valley. Our last rainfall was .4″, and after transplanting a tree afterword I saw the ground had only gotten moist about 1″ down-powder dry soil beneath.

I forget where I found them (probably Lifehacker), but some recent pictures of the US taken by the Gravity Recovery and Climate Experiment satellites show in stark maps the bubble of drought we seem to find ourselves in right now. The first map shows soil surface moisture, moisture in the first centimeter of soil. Look for the little dark red blob right on top of Middlebury. (click on maps for larger view)

The next shows root zone soil moisture, the top meter (39″) of soil.

This final map shows ground water in shallow aquifers (like the well at my house!).

I’ll include the overall map of all three maps, which give a legend to the colors. The explanation is as follows (and is quite scary!)-“The maps do not show an absolute measure of wetness, or water content. Instead they show how water content in mid-September 2015 compares to the average for the same time of year between 1948 and 2012. Dark red represents areas where dry conditions have reached levels that historically occur less than 2 percent of the time (once every 50 or more years).” Note how we are in the dark red in all three maps.

If you have a little bit of time, by all means read how gravity sensing satellites can figure out how much water is in the earth. In a nutshell, it’s two satellites seperated by 139 miles, and sensing how much they move towards or away from each other as they orbit minute changes in gravity from earth can be measured. The complete explaination is at http://earthobservatory.nasa.gov/Features/GRACE/ .

Hope is on the way, though. We’re looking at a pattern change, with a cold front moving into the area and drawing moisture into the region, possibly an inch of rain or more. That’s a good start. Here’s a good rundown from the Northeast River Forecast Center.

Funny, considering how wet it was in late spring, when it was almost too wet to do anything outside. The High Plains Regional Climate Center (kick ass website for weather geeks!) maps show we have 25% of the normal precipitation in the last two months, that’s a 6″ deficit of rainfall.

A general rule of thumb I can’t find a reference for but I always tell anyone is that Vermont plants need a 1/2″ of rainfall per week for optimum growth. We’ve had only about 1″ in all of August, and only 1″ in July. Most of that falling in one day, leaving our clay soils to dry out and become nearly resistant to small rainfalls.

The early leaves you see falling are signs of that. Trees in temperature zones such as ours develop wide, spreading root systems, not going too deep in search of water or nutrients. In fact, much of our campus is on ledge, with very little topsoil available, meaning plants need to go shallow and wide to root into the ground.

(My unsubstantiated theory is that Middlebury was founded where it is because of the ledge-poor soils make poor farmland, and why waste valuable agricultural soils and farmland on something as unimportant as a college? Farmland in 1825 was precious, hard earned space, so let the geeks have the hill, we’ve got crops to harvest)

These wide spreading root systems enable fast, efficient uptake of water and nutrients in poor soils and a short growing season. In ordinary years, this is ideal, but in dry years, this strategy can be costly. As you can imagine, the shallow soils dry quickly, and the plants don’t have the deep extensive root systems to find moisture in the lower soil profiles. Trees are gamblers, and they’ve got a losing hand this year.

Flowers and other perennials show stress by wilting-the curling of the leaves cut down on the loss of water through the stomata (transpiration, if you want to flash back to high school biology). Trees react like that too, but also have the ability to shed leaves. We are seeing this now, and it may cause an early fall. The inner leaves on trees turn color and fall away, a survival mechanism. Inner leaves in the crown are not as efficient, they don’t photosynthesize as well, and therefore are not as “useful” to the tree as the outer, younger leaves. In desperation, the tree will shed the inefficient leaves ,brutally choosing the younger leaves to use the precious remaining water they have remaining.

We’ve had a little bit of rain this weekend, and more is coming, so luck it will come in time to prevent a wholesale dropping of leaves before your parents come up for fall family weekend. Snake Mountain above my house is starting to turn brown along the ledges, though, though, so lower expectations while you can.

Snake Mountain, early September. Note the brown stretches of foliage, probably on ledge.

Pick up any plant biology book, and they consistently list the three macro nutrients all plants need as N, P, and K, the chemical symbols for Nitrogen, Potassium, and Phosphorus. But really, what we share with plants is a need for ‘macro’ macro nutrients, something so profoundly necessary that the books don’t even feel the need to list them, and they form the backbone of all life. We’re talking about C, H, and O, or Carbon, Hydrogen, and Oxygen.

The carbon and the oxygen are easy, the plants are getting that in the air we breathe. It’s the Hydrogen that’s been stressing me out lately. Plants obtain it solely from water, through photosynthesis. I always remember my snide remarks in the retail garden center world, when a customer would ask me what kind of fertilizer to buy with their new purchases. For the most part, I’d tell them the single greatest thing they could do would be to water.

How much? It’s a good question with no real definitive answer. I remember from who knows where that gardens in the northeast need about 1/2″ of rain a week in the growing season, and an article on strawberry production I found says about the same (actually .63″). Trees need quite a bit more, though, as they have much more extensive roots throughout the soil horizon. Plan on 2″ of rain a week. I found a handy online calculator to do the math, but here’s a quick answer. A newly planted tree with about a 2″ trunk, should have a 5′ x 5′ zone watered around it, so that’s about 30 gallons, pretending to be a 2″ rain.

Sounds a little high, but the wild and woolly world of plants is never easy. Last year we were averaging 4″ of rain a month, and we didn’t have to do any supplemental watering. On cloudy days plants don’t transpire, or lose water, at as great a clip, so maybe last year it was fine.

Or not. We’re running around like chickens with our heads cut off right now, watering every tree we’ve planted for the last 3 years. (that’s a lot) All of our recently planted trees are showing drought stress, and I’m wondering if I hadn’t watered enough in the last 2 wet years to well establish the trees. When watering, it is best to water a lot all at once, so that the roots have ample moisture and can grow long and deep. Too little water, and the tree keeps its roots near the surface, where the water is, and this makes it less drought resistant in the long run.

Gator Bags for Watering

We water all trees with 40-50 gallons of water about every 2 weeks. We use two gator bags zipped together, and they drain over the course of about a day. We hand water any tree we missed, and then gator bag it. In this heat and drought, I’d like to water weekly, but I’ve been checking the ground around the trees, and I think we’re keeping up.

Another good trick I learned once when hand watering is to watch the ground as it absorbs water from the hose. I think this is the one of the Eliot Coleman gardening books, but I loaned my copy out and now it’s gone. Once the ground starts to get saturated, the top gets glossy. Take the hose off that spot, and the glossiness will disappear. If you can count to 3 before the glossiness is gone, the ground is moist enough.

Drought stress symptoms in Birch

identifying drought stress in plants can be tricky, especially in herbaceous plants like annuals and perennials. Woody plants are easier. The inner leaves of the tree turn yellow and fall off. I find this remarkable. It isn’t like trees have brains, but here they are smart enough to drop the inner, less efficient leaves, to conserve its precious water for the maximally producing outer leaves. By the time your plants are showing symptoms of drought, obviously much damage is done. Plants are pretty hardy, so even with serious problems the tree will probably be fine.